1. Field of the Invention
This invention relates to porous polytetrafluoroethylene (hereinafter PTFE) materials having the property of rapid recovery and a method for producing these materials. The microstructure of the porous PTFE material consists of nodes interconnected by fibrils, substantially all of the fibrils having a bent or wavy appearance. Articles made from these materials are particularly suitable for use in the medical field, but are also useful in other areas such as filtration and fabric applications.
2. Background of the Invention
Strong, porous PTFE products and their method of manufacture were first described in U.S. Pat. No. 3,953,566. Such products have found widespread acceptance in a myriad of fields. They are used in the medical field as replacement veins and arteries, as patch materials, as sutures and as ligaments. They have also found use in the fields of waterproof and breathable clothing, filtration, sealants and packings, and in threads and filaments for weaving and sewing. These products possess a microstructure of nodes interconnected by fibrils.
U.S. Pat. No. 3,962,153 discloses porous PTFE products with a very fine microstructure and very high strength as well as a process for making the same. U.S. Pat. No. 4,402,516 discloses porous PTFE products with a coarse microstructure but still maintaining the desired high strength. The products disclosed in these patents, like those disclosed in U.S. Pat. No. 3,953,566, have a microstructure of nodes interconnected by fibrils.
The products of the above mentioned patents are relatively inelastic. If they are stretched any appreciable amount they become deformed and will not regain their unstretched dimensions.
U.S. Pat. No. 4,443,511 discloses a method of making a laminated fabric composed partly of porous PTFE that has improved elastic properties. This patent, however, only discloses how to make a stretchable laminated article but does not teach how to provide porous PTFE with the property of rapid recoverability.
In the field of medical prostheses there have been a number of patents directed to tubular products that have elastic properties. U.S. Pat. No. 3,142,067 to Liebig describes a vascular prosthesis comprising a tubular fabric body made of Dacron in which crimps have been made throughout the length of the tube so that the final product demonstrates an elastic accordion-like behavior and is also said to possess flexibility and freedom from kinking under flexure and bending. U.S. Pat. No. 2,836,181 to Tapp similarly describes a nylon tube in which crimps have been made throughout the length of the tube so that it is resistant to kinking or collapsing.